The process of manufacturing of Polyolefin, namely polyethylene (PE) and polypropylene (PP), involves use of various additives such as antioxidants, heat stabilizers, UV stabilizers, acid scavengers, antistatic agents, or any other additive to maintain or enhance the performance of the final polymer. In addition to this special additives are used such as crystallinity modifiers which further augment some of the properties of the resin such as increase in clarity of polymers, cycle time reduction by way of increasing the Tc or the polymer exhibits two Tm one at lower temperature and second one at higher temperature thereby broadening the processing window of especially semi crystalline polyolefin polymers. This type of property of a polyolefin polymer increases its application areas and processor can make niche products.
However, to achieve such properties in a polymer requires addition of number of chemical compounds known as additives and commercially a manufacturing unit spends more capital expenditure to install number of bins for individual additives to dose the same during extrusion stage. Therefore, the call of the day is that if one can use a single additive having a capability of performing two functions can lead to trim down the capital expenditure by slashing the number of bins to be installed in a manufacturing unit.
Synthesis of various polymers involves use of a different catalyst, co-catalyst and promoters. Though now-a-days the activity of these catalyst and co-catalyst system used in synthesis of polymers is high but still the catalytic residues left over from the reactions can even now provoke the multitude of post reactor difficulties. Most of the catalysts used for production of Polyethylene and Polypropylene belong to family of Zeigler Natta Catalysts. Ziegler-Natta catalysts utilize transition metal and late transition metal salts of group III and IV of the periodic table supported on Magnesium Chloride and alkyl aluminums and/or chloride containing alkyl aluminum as co-catalysts. It is particularly the chloride associated with these catalysts, co-catalysts and support which can be corrosive to the melt processing equipment and can reduce the thermal and light stability of the polymers in which they are contained and can also promote the degradation of the polymer chains in the finished material. The presence of chloride ions in PP and PE can result in the formation of hydrochloric acid [HCI] and other acids if not properly scavenged. Hydrochloric acid can degrade the polymer and produce unwanted color formation (yellowing) in the pellets. To neutralize the effect of catalyst or co-catalyst residue acid scavengers are used in ppm level in polymer matrix. Scavenger additives are added to bind up chloride [Cl−] ions left from the co catalysts.
Different types of acid scavengers are available and some of the commonly used acid scavengers are the metallic stearates, metallic oxides, synthetic hydrotalcites etc. These metallic stearates are compounds of long-chain fatty acids with metals of different valencies. The most important metallic stearates, in terms of quantity, are the metallic stearates of, Sodium, aluminium, calcium, magnesium and zinc. Apart from their function to neutralize the acidity, they also work as internal and external slipping/lubricating agents.
U.S. Pat. No. 3,539,306 discloses a process for preparation of hydrotalcite which compromises mixing an aluminum component such as magnesium salt in an aqueous medium in presence of carbonate ion and thereafter recovering the resultant product.
WO03/059917 relates to invention describing synthesis of novel synthetic hydrotalcites and their uses. Also, synthetic hydrotalcites can be made from organic anions longer than C4, and also from organic anions with functional groups including saturated carboxylates of C6, C8, C10 and C18, straight chain acids; aromatics such as benzoates, chloro benzoates etc.
Japanese patent application no. 96-189168 discloses naturally occurring hydrotalcites containing a carbonate anion were used in polypropylene synthesis, along with other additives, and are said to give good melt flow index, flexural modulus and izod impact strength.
EP0910131 describes the use of naturally occurring hydrotalcites containing carbonate anion in an ethylene vinyl acetate copolymer and are said to produce a film with good adhesion and barrier properties.
JP86296799 patent discloses use of naturally occurring hydrotalcites containing carbonate anion in linear low density polyethylene and said to produce film which has thermal insulating properties and good tensile strength.
US20090292052A1 relates to process for preparing calcium carbonate hydroxodialuminates which having hexagonal platelet shaped crystal habit and further discloses the aluminates thus obtained in compositions and stabilizer systems and to the use thereof.
Polypropylene is known to have three crystalline phases, α, β and γ phases besides amorphous phase. Polypropylene crystallizes to α form (monoclinic) which is the most thermodynamically stable form. Polypropylene, however, may also crystallize in the β-form (hexagonal) and in γ-form (orthorhombic). The β-modification is characterized by improved mechanical properties, in particular improved impact strength and improved resistance to stress cracking. Another class of additives incorporated into Polyolefins are Nucleating agents.
Nucleating agents are used in polymer resin to manufacture of plastic articles by various methods, including by injection or extrusion molding. It helps to achieve a polymer significant cycle time reduction in the molding process compared to using non nucleated polymer. Cycle time reduction can be achieved in molded part by inducing in the resin a higher Tc (crystallization temperature). This decreases the necessary cooling time and facilitates ejection of the articles from the mold at a faster rate than would be possible without the use of a nucleating agent. Another class of nucleating agents used specifically for polypropylene are the beta nucleating agents. They lead to increase in impact strength, lower melting temperature and possibility of altogether different set of applications.
EP0177961A2 discloses the process by which β-modification is achieved by shear induced crystallization or by crystallization under temperature gradient or by adding specific β-nucleating agents, such as quinacridone pigments. These quinacridone pigments even when added in low amounts leads to discoloration in polypropylene.
U.S. Pat. No. 5,231,126A and DE 3610644A1 discloses two component type beta nucleating agent and it consisted of a mixture of a organic dibasic acid, such as pimleic acid, azelaic acid, o-phthalic acid, terephthalic and isophthalic acid with an oxide, hydroxide or acid salt of a Group II metal e.g. magnesium, Calcium, Stronium etc. which when employed in Polypropylene matrix gave beta crystalline structure. Drawback of this prior art is that insufficient reproducibility effect of the two-component β-nucleating agent.
EP0682066A1 discloses the method to prepare in situ generated β-Nucleating agent for increasing the content of β-modification in polypropylene.
The beta nucleation effect of various dicarboxamides, in particular N,N-dicyclohexyl-2,6-napthalenedicarboxamide is described in EP-0557721. The disadvantage of this nucleator is the high starting material costs and complicated synthetic steps involved in preparation.
EP0682066A1 discloses one component β-nucleating agent preparation, an attempt for achieving a more reliable β-modification. A drawback of one component β-nucleating agent is that it contains 1 mol of crystal water which tends to decrease the effect of β-nucleation.
JP06279378 discloses the compound useful as a β-crystal nucleus agent for crystallizable PP resin easily, efficiently and in a high yield by subjecting a naphthalene dicarboxylic acid dialkyl and an amine to ester-amide exchange reaction.
Polymer 49 (2008) 2745-2754 demonstrates the use of cadmium bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate (BCHE30) as an effective β-nucleating agent for isotactic polypropylene.
JAPS 123 (2012) 108-117, discloses use of Hexahydrophthalic barium (HHPA-Ba) as β-nucleating agent.